envelope
- 01 A2 Elementary
a flat paper container used for mailing letters or cards.
a flat, usually rectangular paper container with a sealable flap, used for enclosing letters or documents for post.
Simple“She licked the back of the envelope and pressed it shut.”
In context“The solicitor handed over a thick manila envelope containing the original deeds to the property.”
PitfallI need to envelope this letter. I need to envelop this letter.The noun is 'envelope' (with an 'e' at the end), but the verb meaning 'to wrap' is 'envelop' (no 'e' at the end).
- 02 C1 Advanced
the limits of what a machine or system can safely do.
the set of performance limits within which a technological system, especially an aircraft, can operate safely.
Simple“The test pilot was careful not to fly outside the safety envelope.”
In context“By incorporating carbon-fibre components, the design team managed to push the performance envelope of the prototype significantly.”
UsageCommonly used in the idiom 'push the envelope' to mean testing the limits of what is possible.
- 03 B2 Upper Intermediate
a layer that wraps around or covers something else.
a natural or artificial covering that encloses an object or structure.
Simple“The virus is protected by an outer envelope made of proteins.”
In context“The building's thermal envelope was upgraded with high-performance insulation to reduce energy loss during the winter months.”
- 04 C2 Proficiency
the way a sound changes in volume over time.
the variation in the amplitude of a sound signal over time, typically defined by attack, decay, sustain, and release.
Simple“He adjusted the envelope on the synthesizer to make the notes sound softer.”
In context“The sound engineer manipulated the ADSR envelope to give the lead synth a more percussive, aggressive character.”
- 05 C1 Advanced
the large fabric bag that holds the gas in a hot-air balloon.
the fabric structure of an aerostat that contains the lifting gas.
Simple“The ground crew checked the envelope for small holes before the flight.”
In context“The hot-air balloon's nylon envelope expanded rapidly as the burners blasted heat into the opening.”
“And around this black hole, there would be this very extended envelope of gas that looks like a star the size of the solar system.”
“But as Gorton put it, “You gotta keep pushing the envelope.”
PIE word *h₁én From French enveloppe. The engineering sense is derived from flight envelope. The verb is from the noun.
See envelop.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.